The ability to accurately measure analytes in the blood, particularly glucose, is important in the management of diseases such as diabetes. Blood glucose levels must be maintained within a narrow range (about 3.5-6.5 mM). Glucose levels lower than this range (hypoglycemia) may lead to mental confusion, coma, or death. High glucose levels (hyperglycemia) cause excessive thirst and frequent urination. Sustained hyperglycemia has been linked to several of the complications of diabetes, such as kidney damage, neural damage, and blindness.
Blood glucose is maintained in many diabetics with routine injections of insulin. Unlike the normal functioning of the body's glucose control systems, injections of insulin incorporate no feedback mechanisms. Controlling glucose levels therefore requires continuous or frequent measurements of blood glucose concentration in order to determine the proper amount and frequency of insulin injections.
Conventional glucose measurement techniques require a part of the body (normally a fingertip) be lanced, milking the finger to produce a drop of blood at the impalement site, and depositing the drop of blood on a measurement device (such as an analysis strip). This lancing of the finger, at typical measurement frequencies of two to four times a day, is both painful and messy for the patient. The pain and inconvenience has additional and more serious implications of noncompliance, in that many patients will not maintain the recommended regimen of blood glucose measurement and thereby run the risk of improper glucose levels and consequent harmful effects.
In short, the inherent limitations of conventional blood glucose measurement techniques mean that patients either suffer this pain and inconvenience or neglect glucose monitoring and suffer the adverse physiological effects of improper glucose control. Thus there is a clear need for a glucose measurement technique that minimizes or eliminates pain and inconvenience to the patient.
One of the methods of reducing the pain and inconvenience of glucose measurement to a patient is to replace the typical lancet with the use of a hollow needle. Needle use has been reported as less painful than lancet use (B. H. Ginsberg, An overview of minimally invasive technologies, Clinical Chemistry 38:1596-1600, 1992). The pain of sampling is further reduced by withdrawing blood through the needle rather than milking the finger, which involves further pain and soreness. Finally, the containment of the blood in the needle yields a much cleaner and convenient test than conventional techniques which require dripping or smearing blood on a test strip.
Currently known glucose measurement devices that use needles are of two types. The first, such as that described in U.S. Pat. No. 4,953,552, use a needle that remains implanted in the body for an extended period of time--several days, in this case. The second type, such as that described in International Patent Publication 94/13203, uses a needle with an electrochemical sensor integrated into its tip. This second type does not withdraw blood or other body fluids and must still be left in the patient's body tissue for 5-100 seconds in order to measure the output signal from the sensor.
The present disclosure provides an advantage over the existing needle glucose sensors described above in that it comprises a hollow needle with which blood is withdrawn from the patient for monitoring. The use of the needle minimizes the pain and inconvenience to the patient. The withdrawal of blood with the needle allows the needle to be rapidly withdrawn from the patient's body.
The present disclosure also describes a glucose injector. Since blood glucose measurement is normally performed prior to insulin injection, this invention optionally allows both the measurement and the injection to be made with a single needle penetration, further reducing the pain to the patient.